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Actually, one caveat is that GCC's optimization info can be rather inscrutable because it's in terms of compiler internal nomenclature. That's a definite area for improvement (or compiling some sort of key to it).

Indeed, GCC optimizes well. Last time I ran a set of Fortran benchmarks, the geometric mean for them was competitive with other compilers on multiple architectures, and some of the benchmarks could have been sped up considerably with specific compiler options or by re-writing a function sacrificing numerical equivalence, which the Intel compiler seemed to do itself.

by srean1 hours ago|

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I am more of an applied mathematician and a complete ignoramus in compiler technology. So I cannot emphasize enough the surprise ... wait I can actually understand what this compiler is saying and this is not clang, this is not supposed to happen on templates heavy code.

This is by no means a humble brag. Kudos to the GCC engineers. Competition with Clang certainly helped.

by StilesCrisis2 hours ago|

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Explaining? How do you get it to do that?

by srean2 hours ago|

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If you turned on specific optimization and warning flags it emitted a lot of useful information to stdout/stderr. It was quite helpful even to a compiler technology ignoramus like me.

It would identify specific loops and would provide reasons why it could not vectorize it, usually some sort of aliasing that it could not rule out. I would then rewrite the code if the rewrite was simple, to make it obvious that such aliasing wouldn't occur. If it wasn't aliasing it was some sort of a cost benefit model that my loop had not crossed.